Add role: 'form' to all form_for calls

[AlexVPopov]

As per w3schools:

Always use <form role="form"> (helps improve accessibility for people using screen readers)

I would like to make a pull request, where all form_for calls get from:

= form_for @<%= resource_name %>, :html => { :class => "form-horizontal" } do |f|

to

= form_for @<%= resource_name %>, :html => { :class => "form-horizontal", :role => 'form' } do |f|

Will such a PR be accepted?

[doabit]

Welcome PR.